Basic knowledge about Wuchereria bancrofti, the etiologic agent of the widespread disease of Bancroftian filariasis, is meager due to its apparent occurrence in nature only in man. Much of our knowledge of the behavior of lymphatic-dwelling filarial worms in the definitive host has been obtained from studies of closely related species of the genus Brugia which occur in a variety of mammalian hosts. Studies have indicated that Brugia pahangi and B. malayi induced lymphatic infections in jirds, Meriones unguiculatus, and these model systems are useful for studies on host-parasite relationships, pathogenesis, general biology and chemotherapeutic and chemoprophylactic aspect of these infections. It has recently been demonstrated that W. bancrofti will mature in the Taiwan macaque, Macaca cyclopis. This work will now be expanded to systemaatically evaluate several species of the genus Macaca as potential laboratory hosts for W. bancrofti. A detailed description of the developmental behavior of this parasite in the primate host will be given. When patent infections are obtained emphasis will be placed on monkey to monkey passage and subsequently further attempts at establishing the parasite in a rodent host will be undertaken. Further aspects of the jird-Brugia system to be studied include the pathogenesis of early infections, routes of larval migration, serologic and immunologic of the host, and the pathology of long-term infections.